Brain (1984), 107, 829-854 CATEGORY SPECIFIC SEMANTIC IMPAIRMENTS by ELIZABETH K. WARRINGTON and T. SHALLICE (From the National Hospital, Queen Square, London WC1N 3BG) SUMMARY We report a quantitative investigation of the visual identification and auditory comprehension deficits of 4 patients who had made a partial recovery from herpes simplex encephalitis. Clinical observations had suggested the selective impairment and selective preservation of certain categories of visual stimuli. In all 4 patients a significant discrepancy between their ability to identify inanimate objects and inability to identify living things and foods was demonstrated. In 2 patients it was possible to compare visual and verbal modalities and the same pattern of dissociation was observed in both. For 1 patient, comprehension of abstract words was significantly superior to comprehension of concrete words. Consistency of responses was recorded within a modality in contrast to a much lesser degree of consistency between modalities. We interpret our findings in terms of category specificity in the organization of meaning systems that are also modality specific semantic systems. INTRODUCTION Neuropsychological and neurological data provide an important source of evidence on the cerebral organization of visual perception, in identifying not only the component processes in the attainment of a meaningful percept, but also the categories into which meaningful percepts are to be classified. It is now generally accepted that a failure of visual identification that cannot be accounted for by impaired sensory processes (or other confounding factors) can occur as a selective deficit. Not only can visual agnosic deficits at the level of perceptual analysis— apperceptive agnosia—be distinguished from those of semantic analysis—associa- tive agnosia—there is also evidence of differentiation at a semantic level. Thus visual agnosia for objects, colours, faces, topography, parts of the body, letters and numbers have all been identified as mutually dissociable deficits and hence it can be inferred that the neural substrates of these categories are also different {see Hecaen and Albert, 1978). There have been pointers to suggest that such classification might be taken a stage further and that a more fine grain categorical organization can be observed within the broad category of visual object agnosia. As yet the evidence is sparse and mainly anecdotal. Nielson (1946) described a patient (C.H.C.) who he claimed had considerably greater difficulty in identifying inanimate objects by sight or touch, and foods except by taste, than in identifying all living things (including flowers). He also 830 ELIZABETH K. WARRINGTON AND T. SHALLICE observed the converse pattern of deficits in a patient (Flora D) who had greater difficulty in identifying 'animate objects' than inanimate objects. Hecaen and de Ajuriaguerra (1956) reported a single case study of a patient with a left hemisphere lesion in whom they observed a category specific visual agnosia; identification of inanimate objects was more impaired than identification of animals. Konorski (1967) extrapolated from such dissociations between cognitive deficits, to distinguish nine 'gnostic fields', one of which was living things. He also speculated that small manipulable objects form a separate category from nonmanipulable objects. More recently Warrington (1981) provided quantitative evidence of a patient (C.A.V.) who had a significantly greater impairment in the identification of the visual re- presentation of concrete concepts as compared with abstract concepts using a word/ picture matching test (T. Shallice and J. McGill, unpublished) in which the abstract words were represented by pictures of concrete objects (e.g. aptitude—man playing a bassoon) of approximately equivalent familiarity and complexity as the pictures representing concrete concepts (e.g. a donkey). The evidence for category specific deficits is more firmly established for auditory-verbal than visual information. Impaired comprehension of colour names and body part names has long been recorded in the neurological literature. Indeed Goodglass et al. (1966), in the first quantitative investigation of semantic word categories, concluded that the selective impairment or preservation of semantic categories occurred not infrequently in an aphasic population. In a single case study Warrington (1975) demonstrated a significantly greater auditory comprehension impairment for concrete words than abstract words and more recently, quantitative evidence of the selective impairment of the comprehension of inanimate object names has been reported (Warrington and McCarthy, 1983). Category specificity, then, has been documented in both the visual and verbal domains, but the relationship between the two is rarely considered. Typically visual object agnosia is viewed only from the perspective of visual processing. Yet the relationship between visual 'semantics' (i.e. knowledge of things), and their verbal equivalent, could well have far reaching theoretical implications. It seems fairly certain that there is not a one to one correspondence between one domain and the other. For instance, it is accepted (and it has occasionally been documented) that verbal comprehension can be intact in patients with a visual object agnosia (Rubens and Benson, 1971; Hecaen et al., 1974). Conversely, patients with word comprehen- sion difficulties—transcortical sensory aphasia—are not necessarily agnosic for visual stimuli (Benson, 1979; Warrington and McCarthy, 1983). Such observations have usually been interpreted in terms of a unitary semantic system that has been specifically disconnected from 'lower level' modality specific perceptual systems (Geschwind, 1965). There are, however, a number of agnosic phenomena which are difficult to interpret in terms of a single semantic system disconnected from particular input modalities, and more easily interpreted in terms of modality specific semantic systems. Thus certain semantic memory impairments leave the patient with a stable but impoverished semantic processing ability. Only a CATEGORY SPECIFIC SEMANTIC IMPAIRMENTS 831 limited set of items can be identified and for other items, at best, only superordinate information is retained (Warrington, 1975; Coughlan and Warrington, 1981). Such a pattern of impairment can occur together with lack of concordance between modalities; it is then most easily accounted for in terms of the degradation of the stored information within two semantic systems rather than a disconnection. Moreover other observations also suggest the existence of independent modality specific semantic systems. Beauvois et al. (1978) have argued that the observations of patients with optic aphasia and tactile aphasia indicate that separate semantic systems for verbal, visual and tactile information exist {see also Beauvois, 1982). In this paper we report 4 patients recovering from a herpes simplex encephalitis in whom clinical observations suggested the selective preservation of the identification of inanimate objects. Our aim in these investigations was to obtain further evidence for the categorical organization and modality specificity of semantic systems. CASE HISTORIES Case 1 J.B.R., a 23-year-old electronics undergraduate, was admitted to the National Hospital on January 24,1980. Two days previously he had had a grand mal seizure following which he became progressively drowsy. On examination he was pyrexial, his neck was stiff and Kernigs' sign was positive. He was confused and disorientated. EEG showed repetitive complexes bilaterally and a CT scan showed widespread low attenuation, maximal in both temporal lobes, that was considered consistent with herpes simplex encephalitis (see fig.). He gradually became more active and alert but he remained very confused and for a period of one week, three weeks after the onset of his illness, he was observed to eat and drink indiscriminately, including nonfood items. He continued to improve slowly and by August 1980 there were no neurological signs of note other than the cognitive deficits described below (a detailed neurological account of this patient has been given by Greenwood et al., 1983). Psychological test findings. J.B.R.'s scores on intelligence tests are given in Table 1. He was totally disorientated in time and place and he was densely amnesic for ongoing events and for events prior to his illness. On recognition memory tests for words and faces he scored at a chance level (Table 1). He was unable to identify contemporary famous faces or names. His perceptual skills were considered TABLE 1. COGNITIVE TEST RESULTS J.B.R SBY. K.B. ING. 14.4.80 7.8.80 28.6.80 28.4.81 11.6.82 Verbal IQ 102 101 95 70 70 Performance IQ 78 103 93 76 58 Arithmetic 12 15 9 4 4 Similarities 11 10 7 3 6 Digit Span 9 7 7 7 6 Vocabulary 9 8 12 3 4 Picture Completion 7 8 7 6 2 Block Design 9 11 10 5 6 Picture Arrangement 4 7 5 6 0 Matrices IQ 99 100 NT 90 70 Recognition Memory Words (n = 50) 29 - 29 NT 23 Faces (n - 50) 30 18 27 25 Performance on WAIS, Matrices and Warrington's (1984) Recognition Memory Tests. 832 ELIZABETH K. WARRINGTON AND T. SHALLICE to be intact (e.g. on the Warrington and Taylor (1978) test of matching usual and unusual view photographs he scored 20/20 correct and 19/20 correct on the Warrington and James (1967) frag- mented letter test). His spontaneous speech was fluent although he used a somewhat limited and repetitive vocabulary; occasional word-finding difficulty was noted and he